EP0412975B1 - Ceramic moulding produced by powder metallurgy, use and preparation thereof - Google Patents

Abstract

A ceramic moulding produced by powder metallurgy including at least one disperse inorganic constituent, incorporated in a phase of aluminium oxide and/or aluminium nitride and/or aluminium oxide nitride, has (a) a length variation of less than U 10%, preferably less than 1%, relative to the basic state, (b) a porosity of less than 15% and (c) grain boundaries free of vitreous phases. Said ceramic moulding is obtained by sintering a green compact containing, beside the dispersed inorganic constituents, at least 10 volume percent of an aluminium alloyed powder which, after treatment by sintering, is partly or completely reacted to produce Al2O3 and/or AlN and/or aluminium oxide nitride, whereby the morphology of the inorganic components dispersed within said moulding are not modified by the sintering process.

Description

Single- and multi-phase moldings with a ceramic matrix are increasingly being used as temperature and wear-resistant components in machine and apparatus construction. Such bodies are either produced using classic ceramic (ie powder metallurgical) processes by pressing and sintering, or they are produced by reacting metallic precursors with a gaseous or liquid phase (see, for example, "Reaction-Formed Ceramics", Am.Ceram.Soc.Bull, 67 (1988) 356). These so-called reaction-bound ceramics have so far been restricted almost exclusively to Si₃N₄ (RBSN) and SiC (RBSC). A further possibility of producing multiphase ceramics in particular is the infiltration of a porous ceramic body with a metallic or ceramic phase (see, for example, Melt Infiltration Approach to Ceramic Composites ", J.Am. Ceram. Soc. 71 (1988) C-96). In In another novel method, a porous ceramic body is grown through by a ceramic phase which is formed by the reaction of a gas with a metallic melt which has access to the porous ceramic preform on one or more sides (see, for example, "Formation of Lanxide Ceramic Composite Materials", J.Mater.Res 1 (1986) 81).

All these ceramic classes and their manufacturing processes have characteristic disadvantages, which the invention described below hardly or only to a small extent. The decisive disadvantage of classically produced ceramics or ceramic composite materials is the high linear shrinkage that occurs between the green body and the end product; it is usually 15 to 25%. This typical shrinkage makes the shape and dimensional accuracy of a molded part problematic, it leads to cracking and other quality-reducing defects. The shrinkage of a ceramic matrix has a particularly negative effect on the structural integrity when reinforcing elements such as fibers, platelets and whiskers or other non-shrinking components are embedded. The high stresses resulting from the shrinkage differences almost always lead to harmful cracks. Another characteristic disadvantage, particularly of the classically produced oxide ceramics, is the formation of a glass-shaped intergranular phase, which accelerates the sintering or densification process, but greatly impairs the mechanical high-temperature properties.

Reaction-bonded ceramics, especially Si₃N₄ (RBSN) and SiC, and also ceramics manufactured using the Lanxide process (including Al₂O₃ and AlN) show little or no shrinkage, but the manufacturing process is significantly affected by the often weeks-long reaction times. Another disadvantage of the RBSN-like ceramics lies in the fact that only bodies with rarely more than 85% of the theoretical density can be achieved, which can be attributed to the nitrogen diffusion which is increasingly reduced as the porosity decreases.

Experience has shown that such a low density results in poor mechanical properties (see also "Review: Reaction-Bonded Silicon Nitride: its Formation and Properties", J.Marter.Sci., 14 (1979) 1017). The production of ceramic composites based on Al₂O₃ and AlN by melting reaction and related The growth of a porous ceramic preform is described, inter alia, in the recently published European patent applications 0155831, 0169067, 0193292 and 0234704. Here too the reaction is very slow. In addition, dimensional control of the body is associated with great effort.

The invention is therefore based on the object of providing a shaped ceramic body which does not have the above-mentioned disadvantages of the known shaped bodies or only has them to a significantly lesser extent.

This object is achieved by a method for producing a powder-metallurgically produced ceramic molded body which consists of at least one disperse inorganic component which is embedded in a phase of aluminum oxide, has a change in length of less than ± 10% compared to the green state, a porosity of less than 15% and glass phase-free grain boundaries, which is characterized in that a mixture of 25 to 50 vol .-% aluminum powder and optionally one or more of the alloying elements Mg, Si, Zn, Pb, Na, Li and Se and a disperse inorganic component , which contains at least 40 vol .-% alumina, based on the mixture, produces, attracts for at least 1 hour and then forms a green body from it and sinters it in an oxygen-containing atmosphere at temperatures between 900 and 1700 ° C.

According to a first embodiment of the invention, the disperse inorganic component consists predominantly or completely of Al₂O₃ in the form of powder, plate or / and needle-shaped particles.

According to a further preferred embodiment, the disperse phase of the shaped body contains mullite, SiC, B₄C, TiC, Si₃N₄ or alloys thereof in the form of fibers, whiskers or platelets, the total amount based on the shaped body being 5 to 50% by volume. The disperse phase is in a mixture with the above-described particles of Al₂O₃ and / or AlN and optionally ZrO₂.

In a further preferred embodiment, the disperse inorganic component additionally contains powder particles from one or more of the carbide phase SiC, B₄C, TiC, WC, TaC and / or the nitridic phase Si₃N₄ and / or the boridic phases ZrB₂ and TiB₂.

By a suitable choice of the pressing pressure used in the production of the body and the ratio of Al₂O₃ to metallic aluminum, the linear shrinkage or expansion can be reduced to less than 1% compared to the green state, as described in Example 1 in more detail.

When sintering between 900 and 1600 ° C in air, the metallic phase connects the Al₂O₃ powder particles (and possibly other inorganic particles) with simultaneous reaction to Al₂O₃. The volume expansion associated with this reaction fills most of the pores present in the compact and compensates for the shrinkage caused by sintering. With a suitable choice of pressure for the green body and ratio of Al₂O₃ (and possibly other inorganic phases or phase mixtures) to Al powder, a change in volume between the green and finished body can be completely avoided. The product can be referred to as reaction-bound Si₃N₄ as reaction-bound Al₂O₃ (RBAO).

The formation of the shaped body according to the invention is surprising since pure Al powder either reacts explosively under pressing and annealing conditions (with extreme Al powder fineness, ie <approx. 10 μm) or swells like a yeast cake without a connection between the resulting Al 2 O 3 particles cause. Ie it was to be expected that no solid body would arise. A powder combination of Al₂O₃ with pure Al, however, leads to a relatively solid, reaction-bound body. The powder form of Al used according to the invention with possibly small amounts of Mg, Si and Zn powder together with at least 40 vol.% Al₂O₃ powder or AlN results in even denser and firmer moldings. Although works by W. Thiele (Aluminum 38 (1962) 707), S. Balicki (Trace Inst.Hutn. 10 (1958) 208), M. Drouzy and C. Mascare (Metallurgical Reviews, 131 (1969) 25) , M. Richard and R. Emery (Fonderie 373 (1977) 389) and from the aforementioned Lanxide applications (see below EP 0234704) that additions of Mg, Na, Se, Zn, Mn and Si in particular reduce the oxidation of Accelerate Al melts, but they should all the more have resulted in a body bloated like a yeast cake. Even when ZnO and MgO were added in amounts between about 0.1 and about 5% by weight, pure Al powder resulted in solid bodies. Especially compared to the products of the Lanxide process, it is surprising that the metallic phase is completely oxidized to Al₂O₃. A possible explanation is provided by the high density of the grain boundaries present in the molded body according to the invention, which are available as oxygen diffusion paths. Another surprise _, for which no explanation has so far been found, is the fact that grain boundaries without glass phases could be observed in the molded article according to the invention: this phenomenon can be observed in at least 30% of the grain boundaries examined.

Sintering is preferably carried out in air at temperatures between 900 and 1550 ° C with a total pressure of 0.05 to 0.3 MPa.

The amount of Al powder used for the production of the green body is 25 to 50% by volume, based on the mixture with the disperse inorganic component. If Al alloy powder is used, it can be used as such with the alloy components specified above or consist of a mixture of the powders of pure aluminum and the alloy elements or the alloys of the alloy elements forming in situ under the sintering conditions. In particular, in this case pure unalloyed Al powder can be added together with oxides of the alloying elements, magnesium in the form of MgO or MgAl₂O₄, Si in the form of SiO₂ and Zn in the form of ZnO in amounts which between 0.1 and 10% by weight, preferably from 0.5 to 10% by weight, of the alloy element can be used. Accordingly, the preferred content of metallic alloy elements in the Al alloys is 0.5 to 10% by weight of Mg and / or Si and / or Mn and / or Zn and / or Pb and / or Se and / or Na and / or Li. The Al₂O₃ powder is advantageously used with a particle size in the range of 1 to 100 microns, preferably 10 to 30 microns as a starting component.

The starting components are homogenized or mechanically alloyed in an attritor and the powder obtained is then processed into the green body. The green body from the metal / ceramic powder mixture can be produced by dry pressing, slip casting, injection molding or extrusion. The grinding or attrition is expediently carried out in a liquid medium which is inert to the components, such as acetone or an alcohol, such as isopropanol.

The sintering stage itself is carried out in an oxygen or nitrogen-containing atmosphere at a pressure between 0.05 and 10 MPa. The range between 0.08 and 0.5 MPa is preferred, very particularly preferably the range between 0.09 and 0.11 MPa.

According to a particular embodiment of the invention, after the sintering treatment, a hot isostatic post-compression is carried out in a pressure transmission medium made of Ar, N₂ or a mixture of Ar and O₂ (HIP).

For the sintering treatment, the green body can usually be warmed up to the actual sintering temperature be heated. However, the warm-up phase can also be omitted and the green body introduced directly into the hot oven at temperatures between 900 and 1200 ° C. and kept at this temperature until the Al powder has reacted at least in part and then cooled. The holding time is preferably set so that a complete conversion of the Al powder takes place. For this purpose, the actual annealing treatment at 900 to 1200 ° C is followed by reheating to 1300 to 1600 ° C to ensure that the aluminum is completely converted.

The ceramic molded body according to the invention can be used as a matrix for embedding whiskers, fibers or other reinforcement forms of different inorganic substances. In this case, 5 to 50% by volume, based on the mixture of disperse inorganic component and Al powder, of fibers, whiskers or platelets are expediently added, which in turn consist of Al₂O₃, mullite, ZrO₂, SiC, B₄C, TiC, Si₃N₄, AlN or alloys of these substances can exist.

In addition to the above-mentioned preferred inorganic component in the form of Al₂O₃ and AlN, powder particles composed of one or more of the carbidic phases SiC, B₄C, TiC, WC, TaC and / or the nitridic phase Si₃N₄ and / or the boridic phases can also be used as the disperse inorganic component ZrB₂ or TiB₂ can be used.

A further improvement in the physical properties of the shaped body according to the invention can be achieved by infiltration of the finished shaped body with liquid aluminum. Here are the still existing Pores filled by the liquid aluminum, so that a completely tight body is achieved.

The ceramic molded body according to the invention is preferably used as a temperature or wear-resistant component in machine, apparatus and engine construction, as a cutting tool or as a bearing and sealing element.

The figure shows the relationship between the linear change in length of the shaped body compared to the green state as a function of the percentage composition of the green body and the isostatic pressing pressure used in the reheating phase. Various compositions of Al₂O₃ in powder form and Al powder were used. Sintering was carried out by sintering at 1150 ° C. for 15 minutes and then reheating in air at 1550 ° C. for 30 minutes. It can be seen that the decreasing content of Al powder increases the isostatic pressing pressure required for the smallest possible linear shrinkage or expansion.

• 1. Die Längenänderung zwischen dem Grünkörper und dem Fertigprodukt ist kleiner als 10 %, sie kann durch geeignete Auswahl der Komponenten auf weniger als 1 %, sogar auf Null eingestellt werden.
• 2. Die geringe Schrumpfung bzw. Ausdehnung zwischen Grün- und Fertigkörper hat zur Folge, daß nichtschrumpfende Einlagerungsphasen wie Whisker, Fasern oder Plättchen den drucklosen Sintervorgang nicht wie in klassisch hergestellten keramischen Matrizes behindern, d.h. der erfindungsgemäße Formkörper kann also unter Vermeidung des Heißpressens zusammen mit Fasern verdichtet werden.
• 3. Die geringe Volumenänderung bei der Glühbehandlung ermöglicht es außerdem, große Teile spannungsfrei herzustellen und
• 4. Grünkörper sehr schnell aufzuheizen, was die Sinterdauer zum Teil erheblich verkürzen kann.
• 5. Die Sintertemperaturen sind mit 900 bis 1200°C erheblich niedriger als bei klassisch hergestellten Al₂O₃-haltigen Keramiken.
• 6. Die Reaktions- und damit Herstellungszeiten sind im Vergleich zu anderen reaktionsgebundenen Keramiken wie RBSN oder RBSC wesentlich kürzer; dies gilt auch gegenüber den nach dem Schmelzreaktionsverfahren (Lanxide-Prozess) hergestellten Keramiken.
• 7. Alle pulvermetallurgischen Formgebungsverfahren sind ohne Probleme anwendbar.
• 8. Der Einbau von ZrO₂ trägt aufgrund der großen Sauerstoffleitfähigkeit des ZrO₂ zu einer beschleunigten und noch vollkommeneren Reaktion der Al-haltigen Bindephase zu Al₂O₃ bei und verstärkt zusätzlich das Fertigprodukt infolge seiner spannungsinduzierten Umwandlungsfähigkeit.
• 9. Die klassische Sinterung Al₂O₃-haltiger Keramiken beinhaltet immer ein mehr oder weniger starkes Kornwachstum, was üblicherweise die Festigkeit beeinträchtigt. Bei der erfindungsgemäßen Keramik bleibt die ursprüngliche, für den Grünkörper eingesetzte Al₂O₃-Teilchengröße nahezu erhalten.
• 10. Der unter 9. aufgeführte Vorteil gilt im wesentlichen auch für anderen eingelagerte Phasen, die aufgrund der niedrigen Glühtemperaturen kaum oder zumindest erheblich geringer mit der Al₂O₃-haltigen Matrixphase reagieren als es bei der klassischen Sinterung der Fall wäre. Infolgedessen bleiben auch hier Morphologie und Größe der eingebauten Partikel erhalten.
• 11. Ein Vorteil besonders gegenüber den nach dem Lanxide-Prozess hergestellten keramischen Verbundwerkstoffen ist die sehr kleine Korngröße (z.T. <1 µm), die im erfindungsgemäßen Körper eingestellt werden kann.

The molded body according to the invention and the way in which it is produced have a number of advantages, which are listed below:

• 1. The change in length between the green body and the finished product is less than 10%, it can be set to less than 1%, even to zero by suitable selection of the components.
• 2. The slight shrinkage or expansion between the green and the finished body has the consequence that non-shrinking storage phases such as whiskers, fibers or platelets result in the pressure-free sintering process do not hinder as in traditionally produced ceramic matrices, ie the molded body according to the invention can be compressed together with fibers while avoiding hot pressing.
• 3. The small volume change in the annealing treatment also makes it possible to manufacture large parts without tension and
• 4. Heating up the green body very quickly, which can shorten the sintering time considerably.
• 5. The sintering temperatures are with 900 to 1200 ° C significantly lower than with classically produced Al₂O₃-containing ceramics.
• 6. The reaction and thus manufacturing times are significantly shorter compared to other reaction-bound ceramics such as RBSN or RBSC; this also applies to the ceramics produced by the melting reaction process (Lanxide process).
• 7. All powder metallurgical shaping processes can be used without problems.
• 8. The incorporation of ZrO₂ contributes to an accelerated and even more perfect reaction of the Al-containing binding phase to Al₂O₃ due to the large oxygen conductivity of ZrO₂ and additionally reinforces the finished product due to its voltage-induced convertibility.
• 9. The classic sintering of Al₂O₃-containing ceramics always includes a more or less strong Grain growth, which usually affects strength. In the ceramic according to the invention, the original Al₂O₃ particle size used for the green body is almost preserved.
• 10. The advantage listed under 9 applies essentially also to other stored phases, which due to the low annealing temperatures react little or at least considerably less with the Al₂O₃-containing matrix phase than would be the case with classic sintering. As a result, the morphology and size of the built-in particles are retained.
• 11. An advantage, particularly over the ceramic composite materials produced by the Lanxide process, is the very small grain size (sometimes <1 μm), which can be set in the body according to the invention.

The following examples further illustrate the invention.

example 1

100 g of a powder amount consisting of fine Al₂O₃ powder (Alcoa CT 1000, d = 1.3 µm), and 25 vol .-% of an Al alloy powder mixture (93 wt .-% Al, 5 wt .-% Si, 2nd % By weight of Mg, 1% by weight of Zn, all from Eckart) were ground for 6 hours in an attritor mill with 3 mm TZP grinding balls in isopropanol or mechanically alloyed. The mixture was then dried in a Rotovap device and then pressed isostatically with pressures between 45 and 900 MPa to form cylinders with the dimensions 1 cm high, 1 cm diameter. They were then exposed to air at 1150 ° C (1st annealing step) for 15 minutes and then at 1550 ° C (2nd Annealing step) annealed. After the first annealing step, the Al₂O₃ powder particles were connected to a newly formed Al₂O₃ phase, which however still contained pearl-like parts of the Al metal phase. After the second annealing step, the samples were bright white and the Al phase was completely converted into Al₂O₃. TEM studies showed that the porosity was less than 10% and that some grain boundaries did not contain amorphous phases.

The same tests were also carried out with volume fractions of 35, 40, 50 vol .-% Al alloy powder. The linear change in annealing (difference in dimensions in the green state and in the finished state) is shown in Fig. 1 of the drawing. From this it is clear that with certain volume fractions (or ratios of metal powder to ceramic powder) a "zero" shrinkage (ie dimensional stability) could be achieved with different pressing pressures. For example, with 25% by volume of Al alloy powder, an isostatic pressure of 950 MPa would result in "zero" shrinkage.

Example 2

Green body samples according to Example 1 were placed in a 1200 ° C. oven without a warm-up phase. The finished samples did not differ from those according to Example 1, i.e. they showed no cracking due to the thermal shock suffered.

Example 3

100 g of a powder mixture of 20 wt .-% with 2 Y₂O₃-doped ZrO₂ and 80 wt .-% Al₂O₃ (pre-alloyed by Toso, Japan, type Super Z) and 30 vol .-% Al alloy powder (as Example 1) were as in Example 1 treated, wherein the pressing pressure was 800 MPa, and then sintered at 1550 ° C for 1 h. The linear shrinkage was <3% and the strength 300 MPa.

Example 4

Two different aluminum powders were used in a series of tests. on the one hand spherical particles with diameters between 20 and 200 µm and more than 99% Al content (Aldrich-Chemie GmbH, Germany) and Al flakes with a size of 30 to 300 µm and a thickness of 3 to 5 µm ( Al, "finely powdered", E. Merck AG, Darmstadt, Germany). 5% by weight of Si, 2.5% by weight of Mg and 1% by weight of Zn powder were added to this powder. The metal powder was mixed with a coarse Al₂O₃ grinding powder of 13 microns (F 500/13 HC Starck, Berlin, FRG) in amounts between 25 and 40 vol .-%. The majority of the tests were carried out using a composition with 35% by volume Al flakes. In two experiments, 10 vol .-% ZrO₂ powder, which was alloyed with 3 mol% Y₂O₃ (TZ-3Y, Toso, Tokyo, Japan) and 15 vol .-% Al₂O₃ platelets (Al-13pl, Showa Aluminum Industries KK, Tokyo, Japan) of the composition containing 35 vol.% Al flakes, which is referred to below as 35 C. The various powder mixtures were ground in the attritor with acetone or isopropanol in UHMW polyethylene containers using TZP grinding balls with a diameter of 3 mm. After attrition for one to twelve hours, the powder mixtures obtained were dried in a rotary evaporator. The mixtures were then isostatically pressed at 200 to 900 MPa to square rods of 24x4x4mm. The test specimens obtained were processed in the green state before the heat treatment to exact dimensions, which were checked with micrometer measurement.

The heat treatment was carried out in a vertical dilatometer (Fa. Bähr Gerätebau GmbH, Hüllhorst, FRG) in air at temperatures between 1000 and 1500 ° C and different heating rates. The development of the microstructure was examined by optical microscopy on partially and fully reacted samples infiltrated with resin. The test specimens for the measurements of the physical properties were subjected to the following heating treatment in a box furnace:

Heating rate: 5 ° C / minute.
Hold for 8 hours at 1200 ° C, hold for 2 hours at 1550 ° C, cool down at 15 ° C / minute.

The samples obtained were ground and polished to the dimension 22x3.5x3.5 mm and then the breaking strength and the chevron notch toughness K _{Ic were} determined by 4-point bending using an inner and outer span of 18 and 6 mm, respectively. The thermal shock behavior was investigated by quenching from different temperatures to room temperature, water and then determining the maintained strength.

During the grinding, the 13 µm Al₂O₃ grains acted as support for the grinding process, so that the Al particles were broken up into very small pieces without the same being welded. The dimensions of the Al flakes were reduced to less than 10 µm after two hours. After 8 hours of attraction, all of the Al particles were below about 5 μm and were homogeneously dispersed without the development of a flaky microstructure. The size of the Al₂O₃ particles decreased to about 1 micron. With a grinding time of more than 8 hours no noticeable changes in the structure were found. After grinding in acetone for 8 hours, only a portion of the metallic aluminum below 1% was oxidized.

The shrinkage of the ceramic shaped bodies obtained, which were obtained from the material which had been ground for 8 hours and heat-treated as described above, was 4% at 400 MPa isostatic pressure and less than 1% at 700 MPa.

The flexural strength of the 35 C specimens iso-pressed at 400 MPa at room temperature was 281 ± 15 MPa, the corresponding K _Ic value was 2.35 ± 0.2 MPa√m. For the samples obtained with the addition of either 10% by volume of 3Y-ZrO₂ powder or 15% by volume of Al₂O₃ plates to the 35 C composition, the K _Ic value was 2.6 or 2, 75 MPa√m.

Example 5

The 40% by volume Al alloy powder containing the attractive mixture according to Example 4 was added 20% by volume about 1 mm long ZrO₂-reinforced Al₂O₃ fibers (Du Pont, type PRD 166) and mixed dry in a tumble mixer. Thereafter, green bodies were pressed therefrom at a pressure of 400 MPa and sintered in air at 1500 ° C. for 2 h. The fibers were then, without having generated matrix cracks, embedded in the Al₂O₃ matrix.

Example 6

100 g of a powder mixture of 65% by volume of AlN (HC Starck, Grade C, approx. 1 μm) and 35% by volume of the Al alloy powder according to Example 1 were as in Example 1 Described attracted, isostatically pressed at 600 MPa and then sintered at 1550 ° C under N₂ for 2 h. The resulting sintered body then showed a shrinkage of <10%.

Example 7

40 vol .-% Al₂O₃ platelets (13 microns in diameter, Showa Aluminum, Tokyo, Japan) were the composition of Example 1, which had been milled for 8 hours in the attritor, mixed with further milling in the attritor for 20 minutes. The dried mixture was iso-pressed at 400 MPa and heat-treated at 1200 ° C for 8 hours. The linear shrinkage was + 2.1% (actually an expansion) and the final density was 88% of the theoretical density of Al₂O₃ (3.96 g / cm³). The open pores were then filled with Al by pressure infiltration at 20 bar in a gas pressure furnace. The breaking strength of the molded body obtained in this way was 420 MPa, the K _Ic value 7.5 MPa / m, measured using the chevron notch technique with 4-point loading using test specimens of 24 × 4 × 4 mm.

Example 8

37 g of pure Al powder (spherical; company Aldrich) are attracted to 63 g of Al₂O₃ (13 µm) for 8 hours in acetone. 100 g of SiC in the form of a powder which contains 30% particles with a size of approx. 5 µm and 20% particles with a size of approx. 20 µm are then mixed in the tumbled mixer in a tumble mixer for 2 hours. The mixture obtained is dried and statically pressed to a green body at 300 MPa. This is subjected to a heat treatment at 1200 ° C for 1/2 hour and at 1400 ° C for 2 hours. The linear shrinkage obtained compared to the green body is 0%. The open pores of the green body obtained are then, as described in Example 7, filled with Al.

Claims (20)

1. Process for the production of a powder-metallurgically produced ceramic formed body, which consists of at least one disperse inorganic component which is embedded in a Phase of aluminium oxide, which displays a longitudinal change of less than ± 10% in comparison with the green state, possesses a porosity of less than 15% and glass phase-free grain boundaries, characterised in that one produces a mixture of 25 to 50 vol.% aluminium powder and possibly of one or more of the alloying elements Mg, Si, Zn, Pb, Na, Li and Se and of a disperse inorganic component which contains at least 40 vol.% of aluminium oxide, referred to the mixture, attrites for at least 1 hour and then forms a green body therefrom and sinters this in an oxygen-containing atmosphere at temperatures between 900 and 1700°C.
2. Process according to claim 1, characterised in that the Al is used with the alloying elements in the form of a pre-alloy or of a powder mixture.
3. Process according to claim 2, characterised in that the content of metallic alloying elements, referred to the amount of aluminium, amounts to 0.1 to 10 wt.% Mg and/or Si and/or Mn and/or Zn and/or Pb and/or Se and/or Na and/or Li.
4. Process according to claim 2, characterised in that the aluminium powder is used as mixture of non-alloyed Al powder with oxides of the alloying elements and Mg is used in the form of MgO or MgAl₂O₄, Si in the form of SiO₂ and Zn in the form of ZnO.
5. Process according to one of claims 1 to 4, characterised in that an aluminium oxide powder is used with a particle size in the range of 1 to 100 µm as disperse inorganic starting component.
6. Process according to claim 5, characterised in that an aluminium oxide particle size of 10 to 30 µm is used.
7. Process according to one of the preceding claims, characterised in that the disperse inorganic component additionally contains ZrO₂ and/or one or more of the carbidic phases SiC, B₄C, TiC, WC, TaC and/or nitridic Phase Si₃N₄ and/or boridic phases ZrB₂ and TiB₂.
8. Process according to one of the preceding claims, characterised in that, to the attrited mixture, there are added fibres, whiskers or platelets of mullite, SiC, B₄C, TiC, Si₃N₄, Al₂O₃ or alloys thereof in an amount of 5 to 50 vol.%, referred to the attrited mixture.
9. Process according to one of the preceding claims, characterised in that the green body is dry pressed, slip cast, injection moulded or extruded from the metal/ceramic powder mixtures.
10. Process according to one of the preceding claims, characterised in that the sintering is carried out in air at temperatures between 900 and 1550°C and 0.05 to 10 MPa total pressure.
11. Process according to claim 10, characterised in that the green body, without heating-up phase, is introduced into the hot furnace at temperatures between 900 and 1200°C, kept at this temperature up to partial or complete reaction of the Al powder and subsequently cooled.
12. Process according to claim 11, characterised in that, after the calcining treatment at 900 to 1200°C, it is heated to 1300 to 1600°C in order to guarantee a complete reaction.
13. Process according to one of the preceding claims, characterised in that, after the sinter treating, it is hot isostatically post-consolidated (HIP) in a pressure transfer medium of Ar, N₂ or a mixture of Ar and O₂.
14. Process according to one of the preceding claims, characterised in that, after the heat treatment, the formed body is infiltrated at 900 to 1700°C with liquid Al.
15. Powder metallurgically-produced ceramic formed body, consisting of at least one disperse inorganic component which is embedded in a phase of aluminium oxide, characterised in that it

    a) displays a longitudinal change of less than ± 10% in comparison with the green state,

    b) possesses a porosity of less than 15%,

    c) possesses glass phase-free grain boundaries and is obtained by sintering of a green body which is produced from an attrited mixture of 25 to 50 vol.% of aluminium powder which can have one or more of the alloying elements Mg, Si, Zn, Pb, Na, Li and Se and from a disperse inorganic component which contains at least 40 vol.% of aluminium oxide, referred to this mixture.
16. Formed body according to claim 15, characterised in that the disperse inorganic component consists preponderantly or completely of powder-, platelet- or needle-shaped particles of Al₂O₃.
17. Formed body according to claim 15 or 16, characterised in that the disperse inorganic component additionally contains ZrO₂ undoped or doped with Y₂O₃ or CeO₂ or MgO or CaO.
18. Formed body according to one of claims 15 to 17, characterised in that it contains dispersed 5 to 50 vol.%, referred to the mixture of disperse inorganic component and Al alloy, of fibres, whiskers or platelets of Al₂O₃, mullite, ZrO₂, SiC, B₄C, TiC, Si₃N₄, AlN or alloys thereof.
19. Use of the formed body according to claims 15 to 18 as temperature- and wear-resistant component in machine, apparatus and engine construction, as cutting tool or as bearing or sealing element.
20. Process for the production of a powder-metallurgically produced ceramic formed body, which consists of at least one disperse inorganic component which is embedded in a phase of aluminium nitride, which displays a longitudinal change of less than ± 10% in comparison with the green state, possesses a porosity of less than 15% and glass phase-free grain boundaries, characterised in that one produces a mixture of 25 to 50 vol.% of aluminium powder and possibly of one or more of the alloying elements Mg, Si, Zn, Pb, Na, Li and Se and a disperse inorganic component which contains at least 40 vol.% aluminium nitride, referred to the mixture, attrites for at least 1 hour and then forms a green body therefrom and sinters this in a nitrogen atmosphere at temperatures between 900 and 1700°C.

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